FREE BOOKS

Author's List




PREV.   NEXT  
|<   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66  
67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   >>   >|  
the carboniferous period. Other groups which once played a great _role_, are now wholly extinct; for instance, the trilobites of the primary, the sauria of the secondary, the nummulites of the tertiary periods. Now, all these modifications of geological progress would entirely correspond to the idea of a pedigree to which the descent theory traces back the whole abundance of forms of organisms. As soon as we seriously accept the idea of a pedigree, each of the two organic kingdoms would throughout form for its classes and species not only one single straight line of descent, but a tree, the branches of which are again ramified in a manifold way; a tree on which single branches--as perhaps that of the class of birds--may leave the main-stem or a main-branch, possibly being a branch destined to a higher development, and on that account held back in the process of development; a tree, finally, on which also branches and twigs can wholly or partly die off, as those of the extinct or reduced groups of organisms. {69} From the point where the geological formations approach the present time, _plant_ and _animal geography_ also assists _geology_ in increasing the weight of the reasons for an origin of organisms through descent. With the tertiary period, the fauna and flora of the globe, which in former periods had a nearly uniform character all over the earth and showed no climatic differences, begin to separate according to climate, zones, and greater continents. This separation becomes distinctly evident in the middle tertiary formations, the Miocene, and much more distinctly in the higher tertiary formations, the Pliocene. The animals, especially the higher vertebrates, of the Pliocene formation on each continent or each larger group of islands, correspond very closely to the now living animals of the same geographical limit, with the exception of being generally of a much larger size. The Pliocene animal world of mammalia of the three old continents, for instance, corresponds exactly, through all its orders, to the present fauna of Europe, Asia and Africa; and that on an average it was built up more stupendously than that of to-day, we can see from the cave-bear and the mammoth. South America is the home of a peculiar order of mammalia--of the edentata, to which belong the sloth, the armadillo, and the like. All its predecessors are to be found also in the Pliocene strata of South America, and only there; and mostly in giga
PREV.   NEXT  
|<   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66  
67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   >>   >|  



Top keywords:

tertiary

 

Pliocene

 

higher

 

organisms

 
formations
 

branches

 

descent

 

mammalia

 

distinctly

 

animal


continents

 

present

 

development

 
larger
 
animals
 
branch
 

single

 

correspond

 

groups

 

America


wholly

 

periods

 

geological

 
instance
 

extinct

 

period

 
pedigree
 
predecessors
 

differences

 
vertebrates

climatic
 

formation

 
armadillo
 

islands

 
showed
 

continent

 

separate

 
separation
 

greater

 

evident


Miocene

 
middle
 

strata

 

climate

 
Africa
 

average

 

orders

 

Europe

 
mammoth
 

stupendously